Applicant claims the priority of Japanese patent application, Ser. No. 11-125612, filed May 6, 1999.
The present invention relates to a carburetor and more particularly to a rotary throttle valve type carburetor.
Recently, even for portable working machines such as lawn mowers, chainsaws, and the like, increasingly strict gas emission regulations have been promulgated. An engine in such a portable working machine is usually provided with a closed type carburetor which may be operated in substantially any orientation without any fuel leakage while maintaining a sufficient supply of fuel to the engine. However, to comply with the emission control regulations, a carburetor which is excellent in durability and stable in fuel supply so that the amount of fuel does not change over time is required.
In the rotary throttle valve type carburetor disclosed in Japanese Utility Model Publication No. 60-19969, a cam groove formed in a lower face of a throttle valve lever connected to a valve shaft is engaged with a ball supported by an upper wall of the carburetor body so as to cover the ball. Accordingly, dust particles or other foreign particles or contaminants rarely enter the carburetor from the exterior, and smooth movement of the ball is assured. However, even in the above-described structure, an engaged part between the ball in the carburetor body and the cam groove in the throttle valve lever is exposed to the exterior and, therefore, there is the potential for foreign particles or other contaminants to enter the carburetor or foul these components. Especially when the foreign particles are stuck between the ball and the cam groove while the machine is not in use for a long period of time, smooth operation is hindered and the amount of fuel delivered from the carburetor to its engine becomes unstable. Further, the ball and the cam groove are likely to wear because they are engaged with each other only at one point. The throttle valve lever is always employed and actuated with a bending force, and over time, bending or inclination of the throttle valve lever can occur which causes a corresponding change in the amount of fuel delivered from the carburetor. Further, because the cam groove is integral with the throttle valve lever, the shape of the throttle valve lever cannot be freely altered.
In view of the above drawbacks, there is a present need in the art for a carburetor which provides smooth and stable operation, with a constant amount of fuel supplied to its engine over time and which has excellent durability.
A rotary throttle valve type carburetor has a carburetor body with an air intake passage, a cylindrical valve chamber formed perpendicularly to the air intake passage, a throttle valve inserted into the valve chamber, and a throttle valve lever which moves and rotates to impart rotation and axial movement to the throttle valve to regulate the flow of fuel and air in the carburetor. The carburetor according to the present invention is characterized in that a plurality of circumferentially extending cam surfaces are formed on the bottom face of the throttle valve generally symmetrical with respect to the axis of the throttle valve, while tapered bores for receiving balls which are adapted to engage with the cam surfaces are formed in the bottom face of the valve chamber. To facilitate assembly, a columnar-shaped fitting jig is inserted into the valve chamber to accurately press-fit the balls into the tapered bores.
Objects, features, and advantages of the present invention include providing a rotary throttle valve type carburetor which provides a consistent and stable fuel supply to an engine over time, resists the entry of contaminants into the carburetor, permits accurate assembly and operation even with errors in or differences between the various balls and tapered bores, provides a simple fitting jig to accurately and consistently press-fit the balls into the tapered bores, is rugged, durable, reliable, of relatively simple design and economical manufacture and assembly and has a long, useful life.